Ubuntu(Linux) and Red Hat
 

Which is the better O.S between Ubuntu and Red Hat installed on a
Pentium 800 mhz III 256MB memory and M.S.I mainboard(P III)?

This is one of those questions thats difficult to answer because its all about personal preferences. Ubuntu is a good Debian based distro and Redhat is a good rpm based one. Try both of them and then pick the one you like. If installing Redhat, don't bother installing Redhat 9 and below because they are legacy distros and upgrades as well as support from Redhat has been stopped. You would be better off installing Fedora.

Yeah, it is a personal reference....

Well my preference goes to Ubuntu!

I like the slick and light design (it can be made to look like a mac osX in no time)... Redhat is too conventional and old styled. Plus the rpm installations... BLEH.

Synaptic, the package installer in Ubuntu, is very good and efficient.
Minor tweaking required in my case at first but then it's all good: by far it was the easiest installation I've been through.

Go for it!

Synaptic also works for Fedora Core or Redhat, so the issue about rpms is really irrelevant. :)